Phenylenediamine derivative, production method thereof and antioxidant for rubber using it as effective constituent

ABSTRACT

A phenylenediamine derivative represented by following formula (I) or (II): ##STR1## wherein R 1  and R 2  each represents a hydrogen atom, a lower alkyl group, or a lower alkoxy group; R 3  represents a hydrogen atom or a methyl group; R 4  represents a methyl group or an ethyl group; and n and m each is 1, 2, or 3; ##STR2## wherein R 1  and R 2  each represents a hydrogen atom, a lower alkyl group, a lower alkoxy group, or a cyano group; and n and m each is 1, 2, or 3, is disclosed. 
     These phenylenediamine derivatives are effectively used as antioxidants for rubbers, which scarcely cause vanishing by evaporation or a thermal denaturation even under a high-temperature condition of 150° C. or higher.

FIELD OF THE INVENTION

The present invention relates to a phenylenediamine derivative, aproduction method thereof, and an antioxidant for rubber using thephenylenediamine derivative as the effective constituent. Morespecifically, the present invention relates to a phenylenediaminederivative which is stable at a high temperature of 150° C. or higher, aproduction method thereof, and an antioxidant for rubber using thephenylenediamine derivative as the effective constituent.

Also, the present invention relates to an antioxidant for acrylicrubbers. More specifically, the present invention relates to anantioxidant for acrylic rubbers capable of giving an excellent heataging resistance to an acrylic rubber vulcanization product by using twokinds of antioxidant compounds.

BACKGROUND OF THE INVENTION

In particular, requirements for high temperature resistant materials orfor longer life materials has been desired in the automobile industry.In rubber-made materials, antioxidants have been so far added intorubbers to cope with these requirements for high temperature resistanceand for longer life materials. However, almost all antioxidantsavailable in these days have been developed for adding mainly into SBRrubber tires or for various plastics materials. These materials areusually used at a temperature of from about 100 to 150° C., so it issufficient that the antioxidants used in these materials have atemperature resistance of up to about 150° C., and there have beenalmost no antioxidants that are assumed to be used at a temperaturehigher than 150° C. Accordingly, when these antioxidants are used at atemperature higher than 150° C., these antioxidants are apt tovolatilize from the surface of the materials making it difficult toprolong the life of the materials.

To avoid such a fault and to make an antioxidant less volatile,increasing the molecular weight of antioxidants has been studied. Someof the commercially available antioxidants at present are considerablyless volatile. However, in such a less volatile antioxidant, thedispersibility of the antioxidant in a rubber is lowered owing to theincrease of its molecular weight. Also, to realize the low volatility ofan antioxidant, an attempt of chemically bonding the antioxidantmolecule to a polymer and an attempt of holding the antioxidant to aporous substance have been carried out, but there have been manyproblems in practical use of these methods and the above-describedattempts have not yet been practically used at present.

In particular, in the case of an acrylic rubber, an antioxidant isincorporated into the rubber for the purpose of prolonging the lifethereof but the antioxidants proposed until now are yet insufficient andmore improvement has been desired.

In order to make an antioxidant function for a long period of time, itis necessary that the antioxidant must remain in a rubber for a longperiod of time and also it is necessary that the antioxidant that trapsa radical therein is stable. To hold an antioxidant in a rubber for along period of time, an attempt of increasing the molecular weight ofthe antioxidant, an attempt of bonding the antioxidant to a polymer,etc., have been practiced until now as described above, but in the caseof using an antioxidant for an acrylic rubber, in particular for anacrylic rubber as a sealing material, such attempts have notsufficiently been able to give a good result and as the case may be, onthe contrary, hasten aging.

In general, aging of a rubber is caused by an oxidation reaction and theoxidation is supposed to be more severe at the surface of the rubber,the molecule of the antioxidant is required to have a moderate mobilitytoward the rubber surface from inner part of the rubber. However, withincreasing the molecular weight of an antioxidant and by bonding anantioxidant to a polymer, the mobility of the antioxidant in the rubberbecomes small, which is considered to be the reason that the desiredeffect is not obtained. Also, in such an antioxidant, it is consideredthat the radical-trapping capacity per parts by weight of theantioxidant is lowered owing to the increase of the molecular weight ofthe antioxidant.

On the contrary, when an antioxidant having a relatively low molecularweight and a high mobility in the rubber is used, although theantioxidant has a sufficient mobility in the system and a highradical-trapping capacity per weight parts of the antioxidant, thevolatile loss of the antioxidant from the surface of the system or theextraction of the antioxidant from the surface of the system into acontact medium, etc., is large, whereby the sufficient effect cannot beobtained.

Furthermore, it has been performed to improve the heat resistance bycombination of plural antioxidants, such as the combination of a primaryantioxidant (radical-trapping agent such as an amine based or phenolbased antioxidant, etc.) and a secondary antioxidant (peroxidedecomposing agent such as a sulfur based or phosphorus basedantioxidant, etc.), but in this case, the function and the object ofeach antioxidant are utterly different.

Also, there is a related art that describes combination of a same kindof antioxidants, the use thereof is not limited to one kind. Itdescribes that antioxidants each having the same performance can be usedtogether, but there is no suggestion on a synergistic effect bycombination of them.

In a chloroprene rubber and NBR, as the case may be, the synergisticeffect is obtained by combination of amine based antioxidants, but thecombination of the amine based antioxidants in the above-described caseis not effective in the case of acrylic rubbers. The reason is asfollows. That is, because the acrylic rubbers are required to be used ata higher temperature (about 150° C.) than the temperature at which thechloroprene rubbers and NBR are used, and also become hard when heatdegradation occurs, there is a fact that conventional antioxidantscannot endure the practical use at such a high temperature.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a phenylenediaminederivative effectively used as an antioxidant which have a property ofless volatility and almost no thermal degradation under ahigh-temperature condition higher than 150° C.

Also, another object of the present invention is to provide a processfor manufacturing the phenylenediamine derivative mentioned above.

And also, another object of the present invention is to provide anantioxidant for acrylic rubber, which can sufficiently attain an agingpreventing action at a higher temperature than a temperature requiredfor acrylic rubbers by the synergistic effect with combination of thesame kind of antioxidant.

The above-described objects are achieved by a phenylenediaminederivative represented by the following formula (I): ##STR3## wherein R₁and R₂ each represents a hydrogen atom, a lower alkyl group, or a loweralkoxy group; R₃ represents a hydrogen atom or a methyl group; R₄represents a methyl group or an ethyl group; and n and m are an integerof 1, 2, or 3.

Also, the above-described objects are further acieved by aphenylenediamine derivative represented by the following formula (II):##STR4## wherein R₁ and R₂ each represents a hydrogen atom, a loweralkyl group, a lower alkoxy group, or a cyano group; and n and m are aninteger of 1, 2, or 3.

Furthermore, the above-described objects are achieved by an antioxidantfor acrylic rubber having a mixture of:

(A) an antioxidant compound represented by the following formula:##STR5## wherein R₁ represents a hydrogen atom or an alkyl group; R₂represents an alkyl group or a cumyl group; and R₃ represents an alkylgroup, and (B) an antioxidant compound represented by the followingformula: ##STR6##

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the infrared absorption spectrum of theantioxidant 1;

FIG. 2 is a graph showing the infrared absorption spectrum of theantioxidant 2;

FIG. 3 is a graph showing the infrared absorption spectrum of theantioxidant 3; and

FIG. 4 is a graph showing the infrared absorption spectrum of theantioxidant 4.

DETAILED DESCRIPTION OF THE INVENTION

Then, the present invention will be described in detail.

The above-described phenylenediamine derivative represented by theformula (I) [hereinafter referred to as the phenylenediamine derivative(I)] is produced by reacting N,N'-diphenyl-1,4-phenylenediamine with astyrene (or styrene derivative) represented by the following formula:##STR7## wherein R₁ and R₂ each represents a hydrogen atom, a loweralkyl group, or a lower alkoxy group; and R₃ and R₅ each represents ahydrogen atom or a methyl group, in the presence of a protonic acidcatalyst.

The styrene (or styrene derivative) represented by the above-describedformula includes 4-(1-propenyl)-1,2-dimethoxybenzene,4-(1-propenyl)methoxybenzene, tert-butylstyrene, α-methylstyrene,styrene, etc., and they may be used singly or as a mixture of them.

The reaction of both compounds is carried out usingN,N'-diphenyl-1,4-phenylenediamine and the styrene (or styrenederivative) in a molar ratio of 1 to not less than 2, in the presence ofa protonic acid catalyst such as concentrated sulfuric acid, phosphoricacid, etc., at a reaction temperature of from about 100 to 200° C.,preferably from about 130 to 160° C. As the reaction solvent, preferablyan aromatic hydrocarbon such as benzene, toluene, xylene, etc., or analiphatic hydrocarbon, etc., but the reaction can be carried out undernon-solvent system. Because the reaction is one kind of a Friedel-Craftsreaction, the reaction in the presence of an aluminum chloride catalyst,which is, as a matter of course, used as the reaction catalyst, may beconsidered but in this case, the unreacted raw material (i.e.,N,N'-diphenyl-1,4-phenylenediamine) cannot effectively be separatedafter the reaction.

The reaction product obtained contains a slight amount of amono-substituted product but the reaction product has almost the desireddi-substituted product or the poly-substituted product. When a mixtureof two or more kinds of the styrene derivatives is used, thesubstituents R₁ to R₄ of the di-substituted product or thepoly-substituted product can be different from each other. Also, when nand m each is 1, the substitution position is generally at thepara-position to the --NH-- group and when n and m each is 2 (or 3), thesubstitution positions are at the ortho-position (and ortho'-position)in addition to the para-position to the --NH-- group.

The phenylenediamine derivative (I) made up of such a di-substitutedproduct or poly-substituted product can be effectively used as anantioxidant for rubber, which is used under a high-temperature conditionof about 150° C. or higher. The phenylenediamine derivative (I) has afeature that the number average molecular weight Mn of not less thanabout 400 and the weight loss when it is allowed to stand for 40 hoursin hot air of 175° C. is in the range of about 30% or lower, preferablyabout 10% or lower. Also, when the phenylenediamine derivative (I) isadded to a sealing material, which is brought into contact with anengine oil, such as an oil seal, an O-ring, a packing, etc., it has alsoa feature of being excellent in the oil-extraction resistance.

Accordingly, the phenylenediamine derivative (I) of the presentinvention can be effectively used as an antioxidant for various rubbershaving various kinds of crosslinking groups, such as acrylic rubbers,NBR, SBR, EPDM, etc. The amount of antioxidant in the rubber compositionis within the range from about 0.1 to 10 parts by weight, preferablyfrom about 0.3 to 5 parts by weight, per 100 parts by weight of therubber.

Also, the phenylenediamine derivative (I) can be, as a matter of course,used in combination with other antioxidant.

The above-described phenylenediamine derivative of the present inventionrepresented by the formula (II) [hereinafter referred to as thephenylenediamine derivative (II)] is produced by reactingN,N'-diphenyl-1,4-phenylenediamine with a benzoyl chloride (or benzoylchloride derivatives) represented by the following formula: ##STR8##wherein R₁ and R₂ each represents a hydrogen atom, a lower alkyl group,a lower alkoxy group, or a cyano group; and X represents a halogen atom.

The benzoyl chloride (or its derivatives) shown by the above-describedformula includes not only benzoyl chloride but also its 4-methylderivative, 4-methoxy derivative, and 4-cyano derivative, etc. Thesereagents can be used singly or as a mixture thereof.

The reaction of both the compounds described above is carried out byusing N,N'-diphenyl-1,4-phenylenediamine and the benzoyl chloride (orits derivatives) shown by the above formula in a molar ratio of 1 to notless than 2 mole, under the presence of an anhydrous aluminum chloridecatalyst, at a reaction temperature of from about 30 to 100° C.,preferably from about 40° C. to 80° C. As a reaction solvent, anaromatic hydrocarbon such as benzene, toluene, xylene, etc., or analiphatic hydrocarbon, etc., are preferably used, but the reaction canbe carried out under non-solvent system.

The reaction product obtained contains a slight amount of amono-substituted product but the reaction product has almost the desireddi-substituted product or the poly-substituted product. When a mixtureof two or more kinds of the styrene derivatives is used, thesubstituents R₁ and R₂ of the di-substituted product or thepoly-substituted product can be different from each other. Also, when nand m each is 1, the substitution position is generally at thep-position to the --NH-- group and when n and m each is 2 (or 3), thesubstitution positions are at the opposition (and o'-position) inaddition to the p-position to the --NH-- group.

The phenylenediamine derivative (II) made up of such a di-substitutedproduct or poly-substituted product can be effectively used as anantioxidant for rubber, which is used under a high-temperature conditionof about 150° C. or higher. The phenylenediamine derivative (II) has afeature that the number average molecular weight Mn of not less thanabout 450 and the weight loss when it is allowed to stand for 40 hoursin hot air of 175° C. is in the range of about 40% or lower, preferablyabout 20% or lower. Also, when the phenylenediamine derivative (II) isadded to a sealing material, which is brought into contact with anengine oil, such as an oil seal, an O-ring, a packing, etc., it has alsoa feature of being excellent in the oil-extraction resistance.

Accordingly, the phenylenediamine derivative (II) of the presentinvention can be effectively used as an antioxidant for various rubbershaving various kinds of crosslinking groups, such as acrylic rubbers,NBR, SBR, EPDM, etc. The amount of the antioxidant in the rubber is fromabout 0.1 to 10 parts by weight, preferably from about 0.3 to 5 parts byweight, per 100 parts by weight of the rubber.

Also, the phenylenediamine derivative (II) can be, as a matter ofcourse, used together with other antioxidant.

Then, the antioxidant for acrylic rubber made up of a mixture ofantioxidant compounds will be described in detail.

As an aspect of the present invention, the antioxidant for acrylicrubber of the present invention is made up of a mixture of (A) anantioxidant compound [hereinafter referred to as the antioxidant (A) orthe antioxidant compound (A)] represented by the formula (A₁), (A₂), or(A₃) and (B) an antioxidant compound [hereinafter, is referred to as theantioxidant (B) or the antioxidant compound (B)] represented by theformula (B₁) or (B₂) as described above.

The antioxidant A has a property of relatively easily mobility inrubber. The antioxidant corresponding to the formula (A₁) includes analkylated diphenylamine (Nocrac ODA, AD-F, trade names, made by OuchiShinko Kagaku K.K.), etc., and the antioxidant corresponding to theformula (A₂) includes N-phenyl-N'-isopropyl-p-phenylenediamine (Nocrac810-NA, a trade name made by the above-described company),N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (Nocrac 6C, a tradename made by the above-described company), etc. Also, the antioxidantcorresponding to the formula (A₃) is obtained by reactingN,N'-diphenyl-1,4-diphenylenediamine with an equi-molar amount ofα-methylstyrene in the presence of a protonic acid catalyst as shown inReference Example 2 described below.

On the other hand, the antioxidant B has a property of less volatilityas compared with the antioxidant A. And when rubber articles are used incontact with oil fluid or the like, anti-extracting property to thefluid is also required. So the chemical structure of this type ofantioxidant is limited to have a diphenylamine structure or anN,N'-diphenyl-p-phenylenediamine structure and further is limited tohave a cumyl group at the end of the aromatic ring of the diphenylaminestructure or the N,N'-diphenyl-p-phenylenediamine structure.

The reason of limiting the structure of the antioxidant B as describedabove is that in addition of the effect of reducing the volatility andthe extraction loss of the antioxidant by means of increasing themolecular weight, the stability of the antioxidant after trappingradicals is improved by the steric hindrance of the cumyl group.

The antioxidant corresponding to the formula (B₁) described aboveincludes 4,4'-bis(α,α-dimethylbenzyl)diphenyl (Nocrac CD, a trade namemade by Ouchi Shinko Kagaku K.K.), etc., and the antioxidantcorresponding to the formula (B₂) includes the compound obtained byreacting N,N'-diphenyl-1,4-diphenylenediamine with α-methylstyrene in amolar ratio of 1 to not less than 2 mole in the presence of a protonicacid catalyst (see Japanese Patent Application No. 9-24460).

The antioxidant compound (A) and antioxidant compound (B) are used at aratio of from 4 to 40% by weight, preferably from 6 to 30% by weight forthe compound (A) and from 96 to 60% by weight, preferably from 94 to 70%by weight for the compound (B), respectively. When the amount of theantioxidant compound (A) is less than the above ratio, accordingly theantioxidant compound (B) is used at a ratio more than the above ratio,the initial anti-aging property becomes insufficient. On the other hand,when the antioxidant compound (A) is more than the above ratio,accordingly the antioxidant compound (B) is used at a ratio less thanthe above ratio, the long term anti-aging property becomes insufficient.

The sum total of the antioxidant compounds (A) and (B) for acrylicrubber is in the range of about 0.2 to 10 parts by weight, preferablyfrom about 0.5 to 6 parts by weight, per 100 parts by weight of theacrylic rubber.

The acrylic rubber containing two kinds of the above-describedantioxidant compounds (A) and (B) is further properly compounded with areinforcing agent or a filler, such as carbon black, silica, etc.; alubricant such as stearic acid, etc.; a crosslinking agent; acrosslinking accelerator, etc., and is vulcanized according to anordinary curing condition.

[Effect of the Invention]

According the present invention, the phenylenediamine derivatives (I)and (II) have an excellent in the dispersability into rubbers and in thethermal stability even in the case of being used under ahigh-temperature condition. So the antioxidants of the present inventioncan be effectively used as antioxidants for rubbers, etc.

The phenylenediamine derivatives (I) and (II) have also an excellentproperty in the point of the oil-extraction resistance even in the caseof being added to a sealing material which is brought into contact withan engine oil, so these phenylenediamine derivatives can be effectivelyused in sealing materials such as oil seals, O-rings, packings, etc.

Also, when the antioxidant made up of a combination of the same kinds ofthe antioxidants, namely (A) and (B), of the present invention is addedto an acrylic rubber and vulcanized, due to the synergetic action of thecombined antioxidants, the excellent heat aging resistance can beimparted to vulcanized acrylic rubber products, which is used at a hightemperature, such as oil seals, O-rings, etc., for a long period oftime.

The following Examples are intended to illustrate the present inventionmore practically but not to limit the invention in any way.

EXAMPLE 1

(Production of Antioxidant 1)

In a 500 ml three-necked flask on an oil bath were placed 52.0 g ofN,N'-diphenyl-1,4-phenylenediamine (Nocrac DP, a trade name made byOuchi Shinko Kagaku K.K.) and 74.9 g of4-(1-propenyl)-1,2-dimethoxybenzene and after sufficiently replacing theatmosphere with a nitrogen gas with stirring, the temperature of the oilbath was increased to 140° C. Thereafter, 5 g of concentrated sulfuricacid was added dropwise from a dropping funnel to the mixture over aperiod of about 30 minutes, and when after finishing the addition, thereaction was further continued for about 15 hours, the viscosity of thereaction mixture was increased with the passage of time. After thereaction was over, toluene was added to the reaction mixture to form atoluene solution, then the toluene solution was poured into an excessiveamount of an aqueous sodium hydroxide solution, followed by stirring,and then a lower layer (aqueous solution layer) formed was separated bya separating funnel. The toluene solution layer obtained was washed withwater several times until the solution became neutral. Finally, thesupernatant liquid was evaporated off to provide 92.5 g (yield 75%) of ablackish brown desired product.

A definite amount of the product obtained was allowed to stand in anair-circulation type oven at 175° C. for 40 hours but in this case, theweight loss was lower than 5% (3.2%). Also, when the product obtainedwas analyzed by a TLC method (using a silica gel plate, developmentsolvent: n-hexane/toluene=1/2 by volume), the raw material componentsremained were not confirmed and although the spot of an impurity whichwas considered to be the mono-substituted product and spots of unknownstructures existed slightly, the greater part of the product was thedesired product. Mn (by a GPC method using tetrahydrofuran as thesolvent): 860 FI-IR (measured by casting on a KRS-5 crystal plate): FIG.1 ¹ H-NMR (CDCl₃, 25° C.):

near 0.9 ppm (CH₃ group)

near 3.8 ppm (OCH₃ group)

near 6.7 to 7.2 ppm(aromatic H)

Presumed structure: ##STR9##

EXAMPLE 2

(Production of Antioxidant 2)

By following the same procedure as in Example 1 except that the amountof N,N'-diphenyl-1,4-phenylenediamine was changed to 78.0 g and 99.5 gof 4-tert-butylstyrene was used in place of the4-(1-propenyl)-1,2-dimethoxybenzene, 139.0 g (yield 80%) of the desiredproduct was obtained.

The weight loss of the product at 175° C. for 40 hours was lower than10% (6.2%) and the behaviors of the product by the TLC method weresubstantially the same as those in Example 1. Mn (by a GPC method usingtetrahydrofuran as the solvent): 700 FI-IR (measured by casting on aKRS-5 crystal plate): FIG. 2 ¹ H-NMR (CDCl₃, 25° C.):

near 1.22 ppm (CH₃ group)

near 7.1 ppm (aromatic H) Presumed structure: ##STR10##

EXAMPLE 3

(Production of Antioxidant 3)

By following the same procedure as in Example 1 except that 62.2 g ofanethol-(p-methoxypropenylbenzene) was used in place of the4-(1-propenyl)-1,2-dimethoxybenzene, 94.6 g (yield 85%) of a blackishbrown desired product was obtained.

The weight loss of the product at 175° C. for 40 hours was lower than10% (8.6%) and the behaviors of the product by the TLC method weresubstantially the same as those in Example 1. Mn (by a GPC method usingtetrahydrofuran as the solvent): 704 FI-IR (measured by casting on aKRS-5 crystal plate): FIG. 3 ¹ H-NMR (CDCl₃, 25° C.):

near 0.88 ppm (CH₃ group)

near 3.8 ppm (OCH₃ group)

near 6.8 to 7.2 ppm (aromatic H)

Presumed structure: ##STR11##

EXAMPLE 4

(Production of Antioxidant 4)

By following the same procedure as in Example 1 except that 76.0 g ofα-methylstyrene was used in place of the4-(1-propenyl)-1,2-dimethoxybenzene, 84.6 g (yield 85%) of a blackishbrown desired product was obtained.

The weight loss of the product at 175° C. for 40 hours was lower than10% (8.2%) and the behaviors of the product by the TLC method weresubstantially the same as those in Example 1. Mn (by a GPC method usingtetrahydrofuran as the solvent): 500 FI-IR (measured by casting on aKRS-5 crystal plate): FIG. 4 ¹ H-NMR (CDCl₃, 25° C.):

near 1.6 ppm (CH₃ group)

near 6.7 to 7.3 ppm (aromatic H)

Presumed structure: ##STR12##

COMPARATIVE EXAMPLE 1

When in Example 4, an aluminum chloride catalyst was used in place ofthe concentrated sulfuric acid catalyst, 30% or more of the rawmaterial, N,N'-diphenyl-1,4-phenylenediamine, remained in the reactionmixture and it was difficult to remove the remained raw material by apurification method.

EXAMPLES 5 TO 8 AND COMPARATIVE EXAMPLES 2 AND 3

    ______________________________________                                                              (parts by weight)                                       ______________________________________                                        Chlorine-containing acrylic rubber                                                                    100                                                     (Noxtite PA404K, a trade name made by                                         Nippon Mektron Ltd.)                                                          HAF Carbon black 60                                                           Stearic acid 1                                                                Antioxidant (shown below) 2                                                   Sodium stearate (NS Soap, a trade name made 0.25                              by Kao Corporation)                                                           Potassium stearate (Nonsoul SK-1, a trade name 0.25                           made by NOF Corporation)                                                      Sulfur 0.2                                                                  ______________________________________                                    

The antioxidant used in each of Examples and Comparative Examples wereas follows.

Antioxidant 1 (Example 5)

Antioxidant 2 (Example 6)

Antioxidant 3 (Example 7)

Antioxidant 4 (Example 8)

Antioxidant 5^(*1) (Comparative Example 2)

Antioxidant 6^(*2) (Comparative Example 3) Note): Antioxidant 5: NocracCD, a trade name made by Ouchi Shinko Kagaku K.K.; weight loss at 175°C. for 40 hours: about 35%

Presumed Structure: ##STR13##

Antioxidant 6: Nocrac DP; weight loss at 175° C. for

40 hours: about 70%

Each acrylic rubber composition obtained by roll kneading the respectivecompounding components described above was press-vulcanized (primaryvulcanization) at 180° C. for 8 minutes, thereafter, subjected to asecondary vulcanization in a hot air circulating oven at 175° C. for 4hours, and formed into a sheet form of 120 mm×220 mm×2 mm.

About each test piece thus formed, the normal-state property (accordingto JIS K-6301) and the compression set (150° C., 70 hours, and 25%compression) were measured and also a heat aging resistance test(measured as the normal state change after 70 hours at 175° C.) wascarried out. The results obtained are shown in the following table.

    ______________________________________                                                 Example         C. Example                                                    5    6       7      8     2     3                                    ______________________________________                                        [Normal-state                                                                   property]                                                                     Hardness (JIS A) 65 64 66 65 64 65                                            Tensile 14.6 14.3 14.8 14.3 14.2 14.4                                         strength (MPa)                                                                100% 4.9 4.6 5.0 4.9 4.7 4.8                                                  Modulus (MPa)                                                                 Elongation (%) 230 240 240 225 230 240                                        [Heat-aging                                                                   resistance test]                                                              Hardness +4 +4 +5 +6 +8 +11                                                   change (point)                                                                Change ratio of -10 -10 -15 -16 -23 -20                                       tensile strength (%)                                                          Change ratio of +2 +4 +6 +8 +11 -2                                            elongation (%)                                                                [Compression set]                                                             150° C., 70 hours 22 24 25 27 29 32                                  ______________________________________                                         In the above table, C. Example: Comparative Example                      

From the results of the heat-aging resistance test described above, itcan be seen that the samples using the antioxidants of the presentinvention can improve the heat aging resistance and the compression setcharacteristics without deteriorating the normal-state property, thatis, the results show the effectiveness of the antioxidants of thepresent invention.

EXAMPLE 9

(Production of Antioxidant 7)

In a 300 ml three-necked flask on an oil bath were placed 5.2 g ofN,N'-diphenyl-1,4-phenylenediamine (Nocrac DP, a trade name made byOuchi Shinko Kagaku K.K.) and 100 ml of toluene and after sufficientlyreplacing the atmosphere in the flask with a nitrogen gas, 6.7 g ofbenzoyl chloride was added dropwise to the mixture from a droppingfunnel. Then, after finishing the addition, 6.0 g of anhydrous aluminumchloride was added thereto slowly. After adding the total amount ofanhydrous aluminum chloride, the temperature of the oil bath wasincreased to 80° C. and while trapping hydrogen chloride generated, thereaction was continued for about 15 hours with stirring.

After finishing the reaction, 100 ml of toluene was added to thereaction mixture and thereafter, the content of the flask was pouredinto 500 ml of distilled water little by little. After adding the totalamount of the content, the organic layer of the upper portion wastransferred into a 300 ml flask and after adding 100 ml of an aqueoussolution of 10% by weight sodium hydroxide to the organic layer, themixture was refluxed. Thereafter, the organic layer was collected andwashed with distilled water using a separating funnel until the liquidbecame neutral. After washing, toluene was distilled off from theorganic layer to provide 4.6 g (yield 49%) of a blackish brown desiredproduct.

A definite amount of the product obtained was allowed to stand in anair-circulation type oven at 175° C. for 40 hours but in this case, theweight loss was lower than 10% (7.8%). Also, product obtained wasanalyzed by a TLC method (using a silica gel plate, development solvent:n-hexane/toluene=1/2 by volume), the raw material components remainedwere not confirmed and although the spot of an impurity which was to bethe mono-substituted product and spots of unknown structures existedslightly, the greater part of the products was the desired product.

Mn (by a GPC method using tetrahydrofuran as the solvent):

468.56

FI-IR (measured by casting on a KRS-5 crystal plate):

    ______________________________________                                        3342 cm.sup.-1  N--H stretching vibration                                       3060 cm.sup.-1 aromatic C--H stretching vibration                             1649 cm.sup.-1 C═O stretching vibration                                   1300 to 1600 cm.sup.-1 vibration originated from                               aromatic ring                                                                near 700 cm.sup.-1 vibration originated from                                   aromatic ring                                                              ______________________________________                                    

Presumed Structure: ##STR14##

EXAMPLE 10

(Production of Antioxidant 8)

By following the same procedure as in Example 9 using 7.5 g of4-cyanobenzoyl chloride in place of benzoyl chloride, 7.1 g (yield 68%)of a blackish brown desired product was obtained.

The weight loss of the product at 175° C. for 40 hours was lower than20% (19.9%) and the behaviors by the TLC method were substantially thesame as those in Example 9.

Mn (by a GPC method using tetrahydrofuran as the solvent):

518.58

FI-IR (measured by casting on a KRS-5 crystal plate):

    ______________________________________                                        3388 cm.sup.-1  N--H stretching vibration                                       3043 cm.sup.-1 aromatic C--H stretching vibration                             2229 cm.sup.-1 C.tbd.N stretching vibration                                   1651 cm.sup.-1 C═O stretching vibration                                   1280 to 1600 cm.sup.-1 vibration originated from                               aromatic ring                                                                near 700 cm.sup.-1 vibration originated from                                   aromatic ring                                                              ______________________________________                                    

Presumed Structure: ##STR15##

EXAMPLE 11

(Production of Antioxidant 9)

In a 300 ml three-necked flask equipped with a reflux condenser on anoil bath were placed 9.2 g of p-anisic acid (p-methoxybenzoic acid) and100 ml of diisopropyl ether and after stirring the mixture, 18.0 g ofthionyl chloride was added dropwise to the mixture from a droppingfunnel. Thereafter, the oil bath was heated and the resultant mixturewas refluxed for 2 hours. The reflux condenser was removed and the flaskwas heated under a reduced pressure to completely remove volatilecomponents.

After returning the pressure in the flask in which p-anisic acidchloride remained to the atmospheric pressure, 7.2 g ofN,N'-diphenyl-1,4-phenylenediamine and 100 ml of toluene were addedthereto, and then by treating the mixture as in Example 9, 7.8 g (yield37%) of a blackish brown desired product was obtained.

The weight loss of the product at 175° C. for 40 hours was lower than15% (14.7%) and the behaviors by the TLC method were substantially thesame as those in Example 9.

Mn (by a GPC method using tetrahydrofuran as the solvent):

528.61

FI-IR (measured by casting on a KRS-5 crystal plate):

    ______________________________________                                        3327 cm.sup.-1                                                                              N--H stretching vibration                                         3031 cm.sup.-1 aromatic C--H stretching vibration                             2836 cm.sup.-1 CH.sub.3 O group C--H stretching vibration                     1651 cm.sup.-1 C═O stretching vibration                                   1300 to 1600 cm.sup.-1 vibration originated from                               aromatic ring                                                                700 cm.sup.-1 vibration originated from                                        aromatic ring                                                              ______________________________________                                    

Presumed Structure: ##STR16##

EXAMPLES 12 TO 14 AND COMPARATIVE EXAMPLES 4 AND 5

    ______________________________________                                                             (parts by weight)                                        ______________________________________                                        Chlorine-containing acrylic rubber                                                                   100                                                      (Noxtite PA404K, a trade name made by                                         Nippon Mektron Ltd.)                                                          HAF Carbon black 60                                                           Stearic acid 1                                                                Antioxidant (shown below) 2                                                   Sodium stearate (NS Soap, a trade name made 2                                 by Kao Corporation)                                                           Potassium stearate (Nonsoul SK-1, a trade 0.25                                name made by NOF Corporation)                                                 Sulfur 0.2                                                                  ______________________________________                                    

The antioxidant used in each of Examples and Comparative Examples wereas follows.

Antioxidant 7 (Example 12)

Antioxidant 8 (Example 13)

Antioxidant 9 (Example 14)

Antioxidant 5^(*1) (Comparative Example 4)

Antioxidant 6^(*2) (Comparative Example 5)

Note): Antioxidant 5: Nocrac CD, a trade name made by Ouchi ShinkoKagaku K.K.; weight loss at 175° C. for 40 hours: about 35% ##STR17##Antioxidant 6: Nocrac DP weight loss at 175° C. for 40 hours: about 70%

Each acrylic rubber composition obtained by roll kneading eachcompounding components described above was press-vulcanized (primaryvulcanization) at 180° C. for 8 minutes, thereafter, subjected to asecondary vulcanization in a hot air circulating oven at 175° C. for 4hours, and formed into a sheet form of 120 mm×220 mm×2 mm.

About each test piece thus formed, the normal-state property (accordingto JIS K-6301) and the compression set (150° C., 70 hours, and 25%compression) were measured and also a heat aging resistance test(measured as the normal state change after 70 hours at 175° C.) wascarried out. The results obtained are shown in the following table.

    ______________________________________                                                  Example        C. Example                                                     12    13       14      4     5                                      ______________________________________                                        [Normal-state                                                                   property]                                                                     Hardness (JIS A) 65 64 66 64 65                                               Tensile 14.6 14.3 14.8 14.2 14.4                                              strength (MPa)                                                                100% 5.0 4.6 4.9 4.7 4.8                                                      Modulus (MPa)                                                                 Elongation (%) 230 240 240 230 240                                            [Heat-aging                                                                   resistance test]                                                              Hardness +5 +5 +5 +8 +11                                                      change (point)                                                                Change ratio of -12 -14 -14 -23 -20                                           tensile strength (%)                                                          Change ratio of +1 +5 +6 +11 -2                                               elongation (%)                                                                [Compression set]                                                             150° C., 70 hours 25 24 22 29 32                                     ______________________________________                                         In the above table, C. Example: Comparative Example                      

From the results of the heat-aging resistance test described above, itcan be seen that the samples using the antioxidants of the presentinvention can improve the heat aging resistance and the compression setcharacteristics without deteriorating the normal-state property, thatis, the results show the effectiveness of the antioxidants of thepresent invention.

REFERENCE EXAMPLE 1

(Synthesis of Antioxidant B₂)

In a 500 ml three-necked flask on an oil bath were placed 78.0 g (0.3mol) of N,N'-diphenyl-1,4-diphenylenediamine and 76.0 g (0.64 mol) ofα-methylstyrene and after sufficiently replacing the atmosphere in theflask with a nitrogen gas, the temperature of the oil bath was increasedto 140° C. Thereafter, 5 g of concentrated sulfuric acid was addeddropwise to the mixture from a dropping funnel over a period of 30minutes and thereafter, the reaction was continued for about 15 hours.In this case, the viscosity of the reaction mixture was increased withthe passage of time. After the reaction was over, toluene was added tothe reaction mixture obtained to form a toluene solution, thereafter, anexcessive amount of an aqueous sodium hydroxide solution was added tothe toluene solution, followed by stirring, and a lower layer formed wasremoved by a separating funnel. The upper layer liquid was washed withwater several times until the liquid became neutral and finally thesupernatant liquid was evaporated off to provide 126.0 g (yield about85%) of a blackish brown desired product.

When the product obtained was analyzed by thin layer chromatography, theraw material components were not confirmed and although a spot of animpurity which was considered to be the mono-substituted product existedslightly, the greater part thereof was the desired product. Infraredabsorption spectra (measured by casting on a KRS-5 crystal plate):

3400 cm⁻¹ : NH group

2966, 2870 cm⁻¹ : CH₃ group

1610 cm⁻¹ : aromatic ring

820 cm⁻¹ : aromatic substituted product

¹ H-NMR (DMSO, 25° C.)

1.6 ppm: CH₃ group

6.7 to 7.3 ppm: aromatic H

REFERENCE EXAMPLE 2

(Synthesis of Antioxidant A₃)

By following the same procedure as in Reference Example 1 except forchanging the amount of α-methylstyrene to 38.0 g (0.32 mol), 97.5 g(yield 86%) of a blackish brown desired product was obtained. When theproduct obtained was analyzed by thin layer chromatography, the rawmaterial components were not confirmed and the desired product only wassubstantially obtained. Infrared absorption spectra (measured by castingon a KRS-5 crystal plate):

3400 cm⁻¹ : NH group

2966, 2870 cm⁻ : CH₃ group

1610 cm⁻¹ : aromatic ring

820 cm⁻¹ : aromatic substituted product

¹ H-NMR (DMSO, 25° C.):

1.6 ppm: CH₃ group

6.7 to 7.3 ppm: aromatic H

EXAMPLE

    ______________________________________                                                              (parts by weight)                                       ______________________________________                                        Acrylic rubber (Noxtite PA404K, a trade name                                                          100                                                     made by Nippon Mektoron K.K.)                                                 HAF Carbon black 60                                                           Stearic acid 1                                                                Antioxidant A.sub.1 (Nocrac AD-F, a trade 1                                   name made by Ouchi Shinko Kagaku K.K.)                                        Antioxidant B.sub.2 (synthesized in Reference 2                               Example 1)                                                                    Sodium stearate (NS Soap, a trade name 2                                      made by Kao Corporation)                                                      Potassium stearate (Nonsoul SK-1, a trade 0.25                                name made by NOF Corporation)                                                 Sulfur 0.2                                                                  ______________________________________                                    

The components described above were roll-kneaded, the kneaded mixturewas press-vulcanized for 8 minutes at 180° C., then oven-vulcanized(secondary vulcanization) for 4 hours at 175° C., and formed into asheet-form test piece of 120 mm×220 mm×2 mm. About the test piece, thevulcanization property according to JIS K-6301, the heat agingresistance test at 175° C. (measurement of the change of the vulcanizedproduct after 70 hours or after 300 hours), and the compression set (25%compression) were measured.

EXAMPLE₂ 16

In Example 15, a combination of 1 part of antioxidant A₂ (Nocrac 6C, atrade name made by Ouchi Shinko Kagaku K.K.) and 2 parts of antioxidantB, (Nocrac CD, a trade name made by the same company as described above)was used.

EXAMPLE 17

In Example 15, a combination of 0.5 part of the antioxidant A₃ and 3parts of the antioxidant B₂ was used.

COMPARATIVE EXAMPLE 6

In Example 15, 2 parts of the antioxidant A₁ only was used.

COMPARATIVE EXAMPLE 7

In Example 15, 2 parts of the antioxidant B₂ only was used.

COMPARATIVE EXAMPLE 8

In Example 15, a combination of 2 parts of the antioxidant A₁ and 2parts of the antioxidant A₂ was used.

The measurement results of the samples of the above-described Examplesand Comparative Examples are shown in the following table.

    ______________________________________                                                 Example     C. Example                                                        15   16      17     6     7     8                                    ______________________________________                                        [Vulcanization                                                                  property]                                                                     Hardness (JIS A) 65 64 65 65 64 65                                            100% 4.9 4.7 4.8 4.2 4.7 4.8                                                  Modulus (MPa)                                                                 Tensile 14.3 14.2 14.8 14.0 14.2 14.0                                         strength (MPa)                                                                Elongation (%) 230 230 225 225 230 225                                        [Heat-aging                                                                   resistance test]                                                              (70 hours)                                                                    Hardness +4 +5 +4 +14 +8 +12                                                  change (point)                                                                Change ratio of -11 -14 -9 -28 -23 -20                                        tensile strength                                                              Change ratio of +6 +8 +1 -20 +11 -14                                          elongation (%)                                                                (100 hours)                                                                   Hardness +12 +16 +10 +26 +20 +22                                              change (point)                                                                [Compression set]                                                             150° C., 70 hours 22 25 24 28 29 27                                    (%)                                                                         ______________________________________                                         In the above table, C. Example: Comparative Example                      

What is claimed is:
 1. A phenylenediamine derivative represented by the following formula (I): ##STR18## wherein R₁ and R₂ each represents a hydrogen atom, a lower alkoxy group, or a lower alkoxy group; R₃ represents a hydrogen atom or a methyl group; R₄ represents a methyl group or an ethyl group; n and m each represents 1, 2, or 3; and at least one of R₁ and R₂ represents a lower alkoxy group.
 2. The phenylenediamine derivative of claim 1, wherein the number average molecular weight Mn of the phenylenediamine derivative is at least about 400 and the weight loss thereof when the compound is allowed to stand in hot air of 175° C. for 40 hours is about 30% or less.
 3. A method of producing a phenylenediamine derivative represented by the following formula (I): ##STR19## wherein R₁ and R₂ each represents a hydrogen atom, a lower alkyl group, or a lower alkoxy group; R₃ represents a hydrogen atom or a methyl group; R₄ represents a methyl group or an ethyl group; n and m each represents 1, 2, or 3; and at least one of R₁ and R₂ represents a lower alkoxy group,which comprises the step of reacting N,N'-diphenyl-1,4-phenylenediamine and a styrene derivative represented by the following formula: ##STR20## wherein R₁ and R₂ each represents a hydrogen atom, a lower alkyl group, or a lower alkoxy group; and R₃ and R₄ each represents a hydrogen atom or a methyl group, in the presence of a protonic acid catalyst.
 4. The phenylenediamine derivative according to claim 1, wherein R₁ represents a lower alkoxy group.
 5. The method according to claim 3, wherein R₁ represents a lower alkoxy group. 